An analysis of the pollen grains in each layer can tell us what types of plants were growing when the sediment was deposited and then inferences can then be made about the climate based on the types of plants found in each layer.
A famous example of such an event is the eruption of the Laki volcano in Iceland in 1783 which caused a dry, sulphurous fog in Europe, blocking the sun and depressing temperatures.
However, some of this type of evidence is anecdotal.
Accounts, artistic depictions, and photographs of advancing and retreating mountain glaciers during recent centuries provide evidence of climate change on more recent timescales.
Famous examples are the retreat of the Rhône and Grindelwald glaciers in the Swiss Alps.
Two well known examples of such ice core projects are the Greenland Ice Core Project and the Vostok Ice Core Project in Antarctica.
Both cores provide climate data for tens of thousands of years.Coral reefs Corals build their hard skeletons from calcium carbonate, a mineral extracted from seawater.The carbonate contains oxygen and the isotopes of oxygen, as well as trace metals, that can be used to determine the temperature of the water in which the coral was formed as well as the composition of the atmosphere at a certain time.Scientist drill cores of sediments buried below the ocean floor in order to get a sequence of changing climate over time.The most important fossils are shells from so called forams (foraminiferan), tiny creatures living in the worlds oceans that produce shells which sink to the ocean floor after the creatures die.Documentary evidence is, however, generally limited to regions with long literary traditions, such as Britain and parts of Europe, China, and to a lesser extent North America.